The Department of Agriculture and Forestry is advising cereal and forage producers to check their cereal fields for the presence of armyworm larvae. Recent outbreaks of the armyworm in neighbouring provinces have been followed by confirmed reports in west Prince County and eastern and southeastern Kings County. The armyworm is primarily a pest of grass and cereal crops and can cause extensive damage to these crops if present in large numbers.
The armyworm feeds at night so the first sign of damage is often missing leaves. During the day, the armyworms hide in crop debris in or on the soil surface. The young armyworm larva is green in colour and moves in a looping motion. As the larva ages, it becomes dark-green to brown in colour with alternating light and dark stripes. A mature larva is approximately 38 mm in length. Most larvae and pupae do not survive the winter in Canada. Consequently, armyworm populations in Canada are mostly dependent on adult moths being blown northward on storm fronts from the Southern US. Armyworm infestations are more common in years where there is cold, wet spring weather and when parasites have less effect on controlling population levels.
When checking fields, growers should pay attention to field borders and, during the daylight hours, look for feeding damage on plants. If damage is noticed, a more detailed examination may be warranted.
Growers may contact the Department of Agriculture and Forestry to confirm the identity of larva suspected of being armyworms and for threshold levels for treatment. If the larva are larger than 31mm and the feeding damage is extensive, a control measure may not be cost effective as the larva will soon pupate and little more crop damage may be expected.